U.S. patent number 3,907,967 [Application Number 05/380,619] was granted by the patent office on 1975-09-23 for method of purifying gases using rotatable plates having a solid reaction surface layer thereon.
This patent grant is currently assigned to Kernforschungsanlage Julich Gesellschaft mit beschrankter Haftung. Invention is credited to Peter Filss.
United States Patent |
3,907,967 |
Filss |
September 23, 1975 |
Method of purifying gases using rotatable plates having a solid
reaction surface layer thereon
Abstract
A method of and apparatus for purifying gases, especially
industrial waste ases, according to which a solid surface layer
adapted to adsorb impurifications is formed on rotatable discs of
which successive portions during the rotation of the discs
temporarily protrude from a liquid containing container. This
layer, when being contacted by the gas to be purified, adsorbs the
impurifications and harmful substances of the gas. the exhausted
portion of the surface layer is replaced successively by a new
surface layer portion formed by wetting the disc portions when the
latter pass through the liquid in the container.
Inventors: |
Filss; Peter (Julich,
DT) |
Assignee: |
Kernforschungsanlage Julich
Gesellschaft mit beschrankter Haftung (Julich,
DT)
|
Family
ID: |
5851598 |
Appl.
No.: |
05/380,619 |
Filed: |
July 19, 1973 |
Foreign Application Priority Data
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|
|
|
|
Jul 25, 1972 [DT] |
|
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2236389 |
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Current U.S.
Class: |
423/210; 423/230;
423/243.01; 96/289; 95/92; 95/107 |
Current CPC
Class: |
B01D
47/16 (20130101) |
Current International
Class: |
B01D
47/00 (20060101); B01D 47/16 (20060101); B01D
053/00 () |
Field of
Search: |
;423/210,230,239,244,247
;55/68,74,387 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Solomon; W. I.
Attorney, Agent or Firm: Becker; Walter
Claims
What I claim is:
1. A method of purifying gases, especially industrial waste gases,
by means of rotatable plates axially spaced from each other by a
few millimeters and partially immersed into a liquid for forming an
adsorption layer on the plates wetted by said liquid for adsorbing
impurities from the gas to be purified, which includes in
combination the steps of: employing as liquid an aqueous solution
adapted on those portions of the rotatable plates which during the
rotation thereof are above the level of the liquid to form a solid
surface layer capable to adsorb impurities and harmful substances
from the gas to be purified between the respective plate portions
which during rotation of the latter are above the level of the
liquid, rotating the plates, forming the solid surface layer,
feeding impure gas between the plates, and removing impurities and
harmful substances adsorbed by said solid surface layer from said
plates and replacing exhausted portions of said layer by a fresh
forming solid layer by immersing the plate portions into said
liquid, said solid surface layer being operable to chemically react
with and bind impurities and harmful substances in the gas to be
purified and passing between said plates.
2. A method in combination according to claim 1, in which as liquid
an aqueous solution is employed which contains a substance adapted
when reacting with said surface layer to bring about a generation
of a gel with a frame structure.
3. A method in combination according to claim 1, which includes the
step of changing the temperature of at least a portion of said
plates for the purpose of forming the solid layer on the plate
portion above the liquid.
4. A method of purifying gases, especially industrial waste gases
by means of rotatable driven plates axially spaced from each other
by a few millimeters and partially immersed into a liquid for
forming a layer on the plates wetted by said liquid for adsorbing
and chemically reacting impurities from the gas to be purified,
which includes the steps of: employing as liquid an aqueous
solution adapted on those portions of the rotatable driven plates
which during the rotation thereof are above the level of the liquid
to form by evaporation of the liquid a solid surface layer capable
to adsorb and to chemically react impurities and harmful substances
from the gas to be purified, forming a solid surface layer above
the level of the liquid, passing the gas to be purified between the
respective plate portions which during rotation of the latter are
above the level of the liquid, and removing impurities and harmful
substances chemically fixed by said solid surface layer from said
rotatable driven plates and replacing exhausted portions of said
layer by a fresh forming solid layer by immersing the plate
portions into said liquid.
5. A method according to claim 4, which includes the step of
changing the temperature of said plates to increase the speed of
forming said solid surface layer and the reaction of said solid
surface layer with said impurities.
6. A method according to claim 4, in which as liquid an aqueous
solution is employed which contains a substance adapted when
subjected to evaporation to bring about the generation of a gel
with a structure rich in pores.
7. A method according to claim 4, in which as liquid an aqueous
solution is employed which contains a substance adapted for the
generation of a frame structure during reaction of said impurities
of the gases with said solid surface layer.
Description
The present invention relates to a method for purifying gases,
especially industrial waste gases, according to which the gases are
passed between plates above the liquid level, which plates rotate
about an axis and immerge in a liquid by which they are wetted, the
plates being spaced from each other by a distance of a few
millimeters. The particles forming the impurifications are adsorbed
by the wetted surface. The present invention also concerns a device
for practicing this method.
A purification of industrial waste gases prior to their emission
into the atmosphere is necessary because such waste gases generally
contain various impurifications and harmful substances. For
separating the impurifications from the waste gases, numerous
methods and devices have become known. The steps employed in this
connection depend on the respective chemical properties and the
degree of dispersion of the impurities to be separated. As far as
the separation of molecular-disperse harmful substances and
impurifications of gases are involved, in particular wet
purification methods have been employed so far. In this connection,
the gases to be purified are cooled and moistened. This has the
drawback that additional steps are necessary to impart upon the
gases the buoyancy necessary for their emission into the
atmosphere. Another drawback consists in the fact that the gases
are charged with moisture and aerosols as it generally occurs when
liquid washers are employed for the wet treatment which affects the
environment in an undesirable manner. It is furthermore known to
free carbon dioxide containing gases from volatile iron compounds
by passing the gases at an increased temperature over suitable
solid materials, such as lime, barium oxide, or the like. This
method is applicable only for the just mentioned purpose and has
the drawback that the regeneration of the employed adsorbing
material has to be effected in a discontinuous manner.
The prior art furthermore comprises methods for precipitating
useful substances or other admixtures from flue gases, according to
which the gases are passed along discs which partly immerge in
water or a chemical liquid and which rotate at such low speed that
they will remain continuously wetted with liquid. With this method,
the particles suspended in the gases are to adhere to the discs.
This method, however, has the drawback that it remained limited to
the employment of liquid adsorbing means.
It is, therefore, an object of the present invention to provide a
method and device which will make it possible safely to separate
impurifications and harmful substances from gases, especially
industrial waste gases, by binding such impurifications and harmful
substances by reaction and adsorption to solid material-surface
layers while it will be assured that the separation can be carried
out by a continuous regeneration of the solid material-surface
layer without interruption.
These and other objects and advantages of the invention will appear
more clearly from the following specification in connection with
the accompanying drawings, in which:
FIG. 1 is a perspective illustration of a device according to the
invention.
FIG. 2 shows a front view of the device of FIG. 1, but with
additional auxiliary devices.
FIG. 3 is a side view of the device of FIG. 1, partly shown in
section.
The method according to the present invention is characterized in
that on the respective portion of the plates which is located above
the liquid level there is formed a solid surface layer which
adsorbs the impurifications and, as the case may be, reacts
therewith. The method according to the present invention is
furthermore characterized in that in the liquid consisting of the
aqueous solution of the surface layer to be formed the adsorbed
impurifications and harmful substances and, as the case may be, the
substances formed during the reaction of these substances with the
surface layer are removed, and the plates are again wetted. The
impurifications and harmful substances contained in the gases are
when contacting the surface layer formed on the discs bound to this
surface layer, while the surface layer, due to the adsorption or
reaction with the particles contained in the gases, is being
transformed and exhausted. The exhausted layer can in the liquid
normally be easily removed, but in difficult instances it can be
removed by means of brushes, scrapers, and the like. Subsequently
the plates are wetted with a fresh solution. From the thus created
liquid film, a new solid surface layer will form due to drying. For
forming the surface layer, expediently water soluble compounds are
selected which bind the substances contained in the gases to the
solid surface layer formed on the plates by the wetting. Thus, the
liquid must be such that also the substances formed during the
reaction of the impurifications and harmful substances with the
surface layer can be removed. In this way it will be assured that
on the plates, following a further rotation through the liquid
bath, the new film and the surface layer suited for the adsorption
and, as the case may be, for the intended reaction will be
formed.
As far as necessary, the plates are heated or cooled fully or
partly. This will bring about that the intended solid surface layer
will quickly form after the plates emerge from the liquid.
Furthermore, it will be assured that the method according to the
invention is carried out at the temperature most favorable for the
respective type of purification. For practicing the method
according to the invention, it is advantageous that the liquid
contains substances which during the evaporation or the reaction
due to the adsorption of the impurifications on the surface layer
will form a gel with a structure rich in pores or a frame-like
structure. As a result thereof, the effective surface of the
adsorbing surface layer and/or the surface layer reacting with the
substances contained in the gases will be enlarged.
A very advantageous device for practicing the method according to
the present invention consists in that the plates are of circular
shape and are firmly coaxially arranged on a hollow tube which is
adapted in any convenient manner to be heated or cooled. As a
result thereof, as far as this may be expedient, the plates can be
heated or cooled in a simple manner. The continuous regeneration of
the exhausted surface layer is effected by slowly turning the
hollow tube and the plates. The device for practicing the method
according to the invention is particularly effective when the upper
portion of the housing extends with slight play over that part of
the plates which projects out of the liquid level. It has
furthermore proved advantageous to make the diameter of the hollow
tube larger than one third of the outer diameter of the plates. To
make the surface of the plates as large as possible, it is
expedient to roughen the surface of the plates in any known manner
mechanically or by etching. Another advantageous step for forming
the surface layer on the plates consists in that on the plates
there are arranged felt layers comprising metal wires or thin
layers of a known solid material having a large surface, or that
the plates have a regular or irregular profile which enlarges the
surface.
If the load exerted on the hollow tube by the plates is so great
that an undesired bending of the hollow tube occurs, supporting
rollers are rotatably arranged in the housing for supporting the
hollow tube and the plates connected thereto.
A preferred embodiment of the device according to the present
invention consists in that the hollow tube projects partially
beyond the liquid level and that above the liquid level on both
sides of the hollow tube in the gap formed by the housing and the
hollow tube there are provided comb-shaped strips which extend into
the vicinity of the hollow tube and engage the spaces between the
plates. These comb-shaped strips extend parallel to the
longitudinal axis of the hollow tube and are connected to the inner
wall of the housing. In order to realize a fast removal of the
layer forming on the plates from the plates, brushes or scrapers
may be arranged within the liquid bath which are in contact with
the surfaces of the plates. Instead of this arrangement, it is also
possible for removing the surface layer after the latter is loaded
to arrange within the liquid bath an ultrasound device known per
se. It is expedient that the feeding of the gas to be purified and
the withdrawal of the purified gas is effected through connections
which are arranged on opposite sides of the housing. In this way it
will be brought about that the gas passes in radial and azimuthal
direction through the spaces defined by the plates above the liquid
level. If the liquid in the container is replaced and withdrawn
continuously, it is expedient that with a continuous feeding-in and
withdrawal of the liquid the feeding is effected at that point of
the housing where the freshly wetted plates emerge from the liquid,
whereas the withdrawal should be effected on the opposite side of
the housing.
The method and device according to the invention are well suited
for separating molecular disperse impurifications and harmful
substances from air or CO.sub.2 -containing waste gases, such as
I.sub.2, and are particularly well suited for substances with
typical acid character, such as HCl and SO.sub.2.
Referring now to the drawings in detail, the arrangement shown
therein comprises a housing 1 in which on a hollow tube 2 rotatably
journalled in the housing there are arranged a plurality of plates
3 which are rotatable about their axes and are spaced from each
other by a distance of a few millimeters. Tube 2 and plates 3 form
a rigid unit with each other. The lower portion of the
container-shaped housing 1 is adapted to receive and contain a
liquid bath 4. The plates 3 immerge into this liquid bath. To this
end, housing 1 is widened in the manner of a bottom based vessel.
The height of the liquid bath 4 is expediently so selected that the
hollow tube 2 divides the level of the liquid bath 4 into two
ranges. The liquid bath 4 is chemically so composed that the layer
5, which during the rotation of the plates 3 is formed on the
plates within the region above the liquid level 11 by wetting and
drying, is suitable for the adsorption of and/or, as the case may
be, for the reaction with the substances which are contained in the
gas to be purified and which are to be separated. As will be
evident from the drawing, the upper portion of housing 1 extends
with slight play around the plates 3. If the gas to be purified
flows from the connection 6 arranged laterally on the housing 1
into the space above the liquid level 11, the gas will flow through
the spaces between the plates 3 and will leave the housing 1
through the connection 7. If desired, it may be expedient, in order
to realize as uniform a distribution as possible of the incoming
gas when flowing into the housing 1, to provide guiding plates in
the feeding connection 6. When the gas passes through the spaces
between the plates 3, the undesired components contained in the gas
are adsorbed by the surface layer 5 which during the rotation of
plates 3 is formed by drying of the wetting liquid. During the
formation of the solid layers 5, which is effected in conformity
with the method according to the invention on the surface of plates
3, the temperature of the gases to be purified which is frequently
above room temperature, will be taken advantage of. If this should
not suffice or if high temperatures favor the desired reaction, a
heating device 8, for instance gas burners, may be provided in the
hollow tube 2. Instead, also an electric or hot steam or hot air
heating device may be provided. The speed of rotation of plates 3
is furthermore so selected that the plates will remain moist only
in a relatively small range above the liquid level 11 and will be
dried in a short time. To prevent a simultaneous heating up of the
liquid bath 4, it may be expedient to provide cooling coils 9
within the bath. In order to realize both, the heating up of the
plates 3 in the respective range of plates 3 above the liquid level
11 and also a cooling of the liquid bath, it is expedient to select
the diameter of the hollow tube 2 relatively great in comparison to
the outer diameter of the plates 3.
To prevent a strong evaporation of the liquid into the gas which
flows above the hollow tube 2, comb-like strips 10 are on both
sides of the hollow tube 2 and above the liquid level 11 connected
to the inner wall of the housing 1 and extend parallel to the axis
of the hollow tube 2. As will be evident from the drawings, the
plates 3 extend between the strips 10.
The rotation of the plates 3 may be effected in a direction which
is opposite to the direction of flow of the incoming gas. This is
indicated by the arrows in FIG. 1. The rotary movement of plates 3
may, however, if this should be expedient, also be effected in the
same direction as the direction of flow of the incoming gas.
As not shown in the drawings, the plates 3 may, if necessary, for
enlarging their surface, be lined with a thin layer of a material
having a large surface, such as pumice or the like. Instead, the
liquid bath may have added thereto a substance which during the
evaporation or during the purification process forms a gel with a
large surface or a frame-structure. To this end, for instance,
waterglass may be used from which during a reaction with acid gases
the large surface frame-structure of silicic acid is formed.
Another possibility to enlarge the surface of the plates 3 consists
in mechanically or by etching roughening the surface of the plates.
If considered necessary, the plates 3 may entirely or partly have a
corrugated or edged profile. In order to make sure that the solid
material adsorption layer formed on the surfaces of the plates will
be very carefully and quickly washed off, there are within the
liquid bath 4 provided brushes 12 (FIG. 2) which on the inside of
the liquid bath 4 are in contact with both sides of the plates.
Instead thereof or in addition thereto, it is also possible at the
lower portion of the housing 1 to provide a conduit 14 for gas
under pressure which leads into the liquid bath 4 and by means of
which the bath is agitated.
If it is expedient continuously to regenerate the liquid, the
feeding line 15 for the liquid is preferably provided on that side
of the housing on which the plates 3 are through the liquid bath 4
rotated to the outside, while the discharge conduit 16 is provided
on that side of the housing on which the exhausted or used-up layer
is removed from the plates 3. The drive and the mounting of the
hollow tube 2 are arranged outside the housing 1 (not shown in the
drawings).
By means of the device according to the invention as described
above, in which ten plates having a diameter of 90 mm and a
thickness of 5 mm are arranged on a hollow tube having a diameter
of 50 mm -- the spacing between the plates being 5 mm --, the
following gas purifications have been effected. The temperature of
the liquid bath was 30.degree.C, while the temparature between the
plates amounted to 100.degree.C. Both temperatures were measured by
means of mercury thermometers. Prior to practicing the method, the
entire device was each time cleaned by means of a washing
solution.
EXAMPLE 1
Iodine containing air was purified by means of the device according
to the invention. The device contained a 10% KIsolution as liquid
bath from which the adsorption layer formed. For producing the
iodine containing air, first ordinary air was at room temperature
saturated with iodine steam by air flowing over iodine crystals.
The partial pressure of the iodine in the added air amounted to
0.25 Torr. With the plates mounted on the hollow tube rotating at a
speed of 8 rph, the following values were obtained:
Relative Iodine con- Relative iodine con- Flow velocity tent prior
to the tent after the gas of the raw gas gas purification
purification ______________________________________ 12 l/h 1 1/100
25 l/h 1 1/100 50 l/h 1 1/20 100 l/h 1 1/4 250 l/h 1 1/2
______________________________________
The relative iodine content was determined calorimetrically by
discoloration of starch paper.
The uniform brown coloration of the bath liquid by I.sub.2 in the
region of the immersed plates indicates that the iodine adsorption
and thus also the gas flow were distributed uniformly over the
individual chambers of the plate packet.
EXAMPLE 2
HCl-containing air was purified by means of NaOH as bath and
adsorbing substance. For producing HCl-containing air, first
ordinary air was charged with HCl by flowing over a 35%
hydrochloric acid; at a flow velocity of 25 1/h, the HCL partial
pressure amounted to 30 Torr. The rotational speed of the plates on
the hollow tube amounted to 12 rph. The following values were
obtained:
Relative HCl con- Relative HCl con- Flow velocity tent prior to the
tent after the gas of the raw gas gas purification purification
______________________________________ 12 l/h 1 1/1500 25 l/h 1
1/350 50 l/h 1 1/25 100 l/h 1 1/3
______________________________________
EXAMPLE 3
During the purification of HCl-containing air under the same
conditions as in Example 2, but with a bath liquid of waterglass
diluted with water at the ratio of 1: 1 (Merck Article No. 5621),
the following values were obtained:
Relative HCl con- Relative HCl con- Flow velocity tent prior to the
tent after the of the raw gas gas purification gas purification
______________________________________ 12 l/h 1 1/500 25 l/h 1
1/500 50 l/h 1 1/50 100 l/h 1 1/20
______________________________________
The exhausted or used-up layer scaled off from the plates in the
manner of fish scales.
EXAMPLE 4
SO.sub.2 -containing air was purified by means of a liquid bath
which contained 100 g of NaOH per one liter of the bath. The
SO.sub.2 --containing air had previously been prepared by passing
air through a piston in which a diluted sulfuric acid dripped onto
sodium sulfite. At a flow velocity of 50 1/h, the partial pressure
of the SO.sub.2 amounted to 6 Torr. At a speed of rotation of 12
rph, the following values were obtained.
______________________________________ Relative SO.sub.2 con-
Relative SO.sub.2 con- Flow velocity tent prior to the tent after
the gas of the raw gas gas purification purification
______________________________________ 50 l/h 1 1/200 100 l/h 1
1/35 250 l/h 1 1/12 ______________________________________
The layer which detached itself from the plates had a character
similar to that of the embodiment of Example 3.
It is, of course, to be understood that the present invention is,
by no means, limited to the specific showing in the drawings and to
the specific examples set forth in the specification, but also
comprises any modifications within the scope of the appended
claims.
* * * * *